Systems and methods for measuring performance parameters related to orthopedic arthroplasty

ABSTRACT

A knee balancing system for measuring performance parameters associated with an orthopedic articular joint comprises a force sensing module and one or more inertial measurement units. The force sensing module comprises a housing that includes an articular surface having a medial portion and a lateral portion, each of which is substantially mechanically isolated from the other. The force sensing module also includes first and second sets of sensors disposed within the housing. The first set of sensors is mechanically coupled to the medial portion of the articular surface and configured to detect information indicative of a first force incident upon the medial portion of the articular surface. The second set of sensors is mechanically coupled to the lateral portion of the articular surface and configured to detect information indicative of a second force incident upon a lateral portion of the articular surface. The inertial measurement unit is configured to detect information indicative of an orientation of at least one of a first bone and a second bone of a knee joint.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/860,409, filed Sep. 21, 2015, which is continuation ofPCT/US2013/068054, filed Nov. 1, 2013, which claims the benefit of U.S.Provisional Application No. 61/803,665, filed Mar. 20, 2013, thedisclosures of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates generally to orthopedic surgery and, moreparticularly, to systems and methods for measuring performanceparameters associated with joint replacement surgeries.

BACKGROUND

For most surgical procedures, it is advantageous for a surgeon tocompare intra-operative progress and post-operative results with apre-operative plan to ensure that surgical objectives are met. In somesurgical procedures, particularly those involving orthopedicarthroplasty, relatively small deviations from a pre-operative plan cantranslate into significant differences in the functionality of thepatient's anatomy. For example, in joint replacement surgery on the kneeor hip, small changes in the positioning of the prosthetic jointcomponents may result in considerable differences in the patient'sposture, gait, and/or range of motion.

In the early years of joint replacement surgery, intra-operativeevaluation of the reconstructed joint was highly subjective. Theevaluation process typically involved the surgeon manual placing the legin different poses and repeatedly articulating the joint through varyingdegrees of flexion and extension of the leg, while testing the range ofmotion and relative stability of the joint based on “look and feel.”This process for intra-operative evaluation was extremely subjective,and the performance of the reconstructed joint was highly dependent onthe experience level of the surgeon. Perhaps not surprisingly, it wasdifficult for patients and doctors to reliably predict the relativesuccess of the surgery (and the need for subsequentcorrective/adjustment surgeries) until well after the initial procedure.Such uncertainty has a negative impact on the ability to predict andcontrol costs associated with surgery, recovery, and rehabilitation.

As orthopedic surgeons and researchers became more familiar with thekinematics and/or kinetics of joint function, techniques forintra-operatively measuring specific joint parameters increased thereliability and repeatability of joint reconstruction surgeries. Forexample, in knee replacement/reconstruction procedures, surgeons havelong sought to ensure that the reconstructed joint is properly“balanced.” A poorly-balanced knee can cause undesired condylarseparation at the femorotibial interface, instability during flexionand/or extension, and malalignment and/or malrotation, potentiallyleading to soft tissue damage, improper/excessive implant wear, andgeneral discomfort for the patient. Knee balancing generally refers tothe collection of intra-operative processes used by the surgeon toensure that the reconstructed knee joint restores proper alignment ofthe leg, appropriate distribution of weight, and stability across a widerange of motion.

There are two conventional techniques for helping orthopedic surgeonsbalance a knee: gap balancing and measured resection. The gap balancingtechnique calls for the surgeon to position the femoral componentparallel to the resected surface of tibia while the collateral ligamentsare equally tensioned. The goal of the gap balancing technique is tomaintain a uniform “gap” between the femoral condyles and tibialarticular surface for a prescribed uniform tension applied by thecollateral ligaments.

The measured resection technique involves resecting the bone based onanatomical landmarks in order to preserve the position of one or more ofthe anatomical axes associated with the knee joint. To do so, thesurgeon makes precision cuts to the bone based on anatomical landmarksof the femur and tibia. During reconstruction of the joint, the surgeonaims to replace the exact thickness of the resected portions to ensurethat the reconstructed anatomy (particularly the anatomical axes ofrotation) matches the original anatomy of the joint as closely aspossible. The theory behind measured resection is that, becauseeverything that is removed is replaced, the original (and ideal) kneebalance is restored. One benefit of this technique is that the femur andtibia can be resected independently of one another, so long as theposition of the reconstructed axis is maintained.

Regardless of the specific knee balancing technique used, many surgeonsrely on measuring devices for independently analyzing/validating certainjoint metrics during the procedure. One of the most useful sets of jointmetrics includes data indicating the forces present at the tibiofemoralinterface. The magnitude and medial-lateral distribution of such forces,for example, can aid the surgeon is determining proper ligament balanceand component placement.

Conventional devices for intra-operatively measuring forces useelectrical transducers embedded within a joint prosthesis. When theprosthesis is inserted into the joint, compressive forces between thetibia and femur mechanically deform a structural element of thetransducer resulting in corresponding change in an electrical output ofthe transducer. The change in the electrical output is converted by aprocessor into a force value, which the surgeon uses to make adjustmentsnecessary to balance the knee.

While such conventional devices may accurately measure instantaneousforce values in certain situations, such devices may still beinadequate. For example, conventional femorotibial force sensors may beinsufficient for measuring the location of medial and lateral forcesrelative to the corresponding articular surface of the force sensor.Furthermore, many conventional prosthetic force sensors do not includesufficient isolation between the medial and lateral hemispheres of thesensor. As a result, it is difficult for the surgeon to preciselydetermine the individual forces applied to the medial and lateralarticular surfaces.

Additionally, conventional force sensing devices and systems areinsufficient in providing the user with ability to combine kinematicand/or kinetic information in order to track the location and magnitudeof the medial and lateral forces with respect to joint angles offlexion/extension, varus/valgus, and internal/external rotation.Further, conventional femorotibial force sensing systems do not providea convenient platform for real-time intra-operative tracking of themovement of the location of the medial and lateral forces as the jointis articulated across the full range of motion. As such, conventionalforce sensing systems don't provide sufficient capabilities for allowingthe surgeon to monitor medial and lateral forces as a function of jointflexion/extension angle and knee alignment.

The presently disclosed systems and methods for intra-operativelytracking joint performance parameters in orthopedic arthroplasticprocedures are directed to overcoming one or more of the problems setforth above and/or other problems in the art.

SUMMARY

According to one aspect, the present disclosure is directed to acomputer-implemented method for tracking parameters associated with anorthopedic articular joint, the method comprising receiving, at aprocessor associated with a computer, first information indicative of aforce detected at an articular interface between a first bone and asecond bone of a patient and receiving, at the processor, secondinformation indicative of an orientation of at least one of the firstbone and the second bone. The method may also comprise estimating, bythe processor, a location of a center of the force relative to a surfaceof the articular interface, the estimated location based, at least inpart, on the first information. The method may further compriseestimating, by the processor, an orientation angle associated with atleast one of the first bone and the second bone relative to a referenceaxis, the orientation angle, based, at least in part, on the secondinformation. The processor may provide third information indicative ofat least one of: the estimated location of the center of the forcerelative to the surface of the articular interface or the orientationangle associated with the at least one of the first bone and the secondbone relative to the reference axis.

In accordance with another aspect, the present disclosure is directed toa force sensing module for measuring kinematic and/or kinetic parametersassociated with an orthopedic articular joint. The force sensing modulemay comprise a housing including an articular surface having a medialportion and a lateral portion, each of which is substantiallymechanically isolated from the other. The force sensing module may alsoinclude a first set of sensors disposed within the housing, the firstset of sensors being mechanically coupled to the medial portion of thearticular surface and configured to detect information indicative of afirst force incident upon the medial portion of the articular surface.The force sensing module may also include a second set of sensorsdisposed within the housing, the second set of sensors beingmechanically coupled to the lateral portion of the articular surface andconfigured to detect information indicative of a second force incidentupon a lateral portion of the articular surface.

According to another aspect, the present disclosure is directed to aknee balancing system for tracking kinematic and/or kinetic parametersassociated with an orthopedic articular joint that comprises aninterface between a first bone and a second bone. The knee balancingsystem comprises a force sensing module, at least a portion of which isconfigured for implantation within orthopedic articular joint. The forcesensing module may be configured to detect information indicative of atleast one force incident upon at least a portion of an articular surfaceof the force sensing module. The knee balancing system may also compriseat least one inertial measurement unit for tracking 3-dimensional jointangles associated with an orthopedic articular joint. The inertialmeasurement unit is configured to detect information indicative of a3-dimensional orientation of at least one of a first bone and a secondbone. The knee balancing system may further comprise a processingdevice, communicatively coupled to the force sensing module and at leastone inertial measurement unit. The processing device may be configuredto estimate a location of at least one force relative to the articularsurface, the estimated location based, at least in part, on theinformation indicative of the force incident upon at least a portion ofthe articular surface of the force sensing module. The processing devicemay also be configured to estimate an orientation angle associated withthe at least one of the first bone and the second bone relative to areference axis, the orientation angle, based, at least in part, on theinformation indicative of the orientation of at least one of the firstbone and the second bone. The processing device may be furtherconfigured to provide information indicative of at least one of: theestimated location of the force relative to the surface of the articularinterface or the orientation angle associated with at least one of thefirst bone and the second bone relative to the reference axis.

In accordance with another aspect, the present disclosure is directed toa force sensing module for measuring kinematic and/or kinetic parametersassociated with an orthopedic articular joint. The force sensing modulemay comprise a housing including an articular surface and a plurality ofsensors disposed within the housing. The plurality of sensors may bemechanically coupled to the articular surface and configured to detectinformation indicative of a force incident upon the articular surface ofthe housing. The force sensing module may also include a processingdevice, communicatively coupled to the each of the plurality of sensorsand configured to receive the information indicative of the forceincident upon the articular surface of the housing. The processingdevice may also be configured to estimate a location of a center of theforce relative to a boundary associated with the articular surface, andestimate a magnitude of the force at the estimated location of thecenter of the force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a diagrammatic view of an exemplary knee kinematicsand/or kinetics monitoring system (embodied as an intra-operative kneebalancing system) consistent with certain disclosed embodiments;

FIG. 2 illustrates a magnified view of an exemplary reconstructed kneejoint with a trial force sensing tibial insert, in accordance withcertain disclosed embodiments;

FIG. 3 provides a schematic view of exemplary components associated witha force monitoring system, such as the knee balancing system illustratedin FIG. 1;

FIG. 4 provides a perspective exploded view of an exemplary trialprosthetic force sensing insert consistent with certain disclosedembodiments;

FIG. 5A provides schematic views of exemplary resistive force detectingtransducers that may be implemented within the force sensing module,consistent with certain disclosed embodiments;

FIG. 5B provides a schematic view of an exemplary capacitor-type forcedetecting transducer that may be implemented within the force sensinginsert, in accordance with certain disclosed embodiments;

FIG. 5C provides a schematic view of another exemplary capacitor-typedesign of a force detecting transducer that may be implemented withinthe force sensing insert, consistent with certain disclosed embodiments;

FIG. 6 provides a perspective exploded view of another exemplary trialprosthetic force sensing insert consistent with certain disclosedembodiments;

FIG. 7A provides a perspective top view of an exemplary force sensingtransducer used in an exemplary trial prosthetic force sensor, inaccordance with certain disclosed embodiments;

FIG. 7B provides a top view of an exemplary force sensing transducershown in FIG. 6A, consistent with certain disclosed embodiments;

FIG. 7C provides a cross section view (facing bottom to top) of anexemplary force sensing transducer shown in FIG. 6A, in according withcertain disclosed embodiments;

FIG. 7D provides a side view of an exemplary force sensing transducershown in FIG. 6A, consistent with certain disclosed embodiments;

FIG. 7E provides a front view of an exemplary force sensing transducershown in FIG. 6A, in accordance with certain disclosed embodiments;

FIG. 8 provides a schematic cross-sectional view of an exemplary gapmeasurement module, consistent with certain disclosed embodiments;

FIG. 9 provides a perspective view of an exemplary trial prostheticforce sensing insert with removable positioning handle, consistent withcertain disclosed embodiments;

FIG. 10 illustrates an embodiment of a user interface that may beprovided on a monitor or output device for intra-operatively displayingthe monitored joint performance parameters in real time, in accordancewith the disclosed embodiments;

FIG. 10A illustrates an alternate embodiment of a user interface thatmay be provided on a monitor or output device for intra-operativelydisplaying the monitored joint performance parameters in real time, inaccordance with the disclosed embodiments;

FIG. 11 provides a flowchart depicting an exemplary process to beperformed by one or more processing devices associated with forcemonitoring systems consistent with the disclosed embodiments;

FIG. 12 provides an exemplary screen shot of a user interface, which maybe provided on a monitor or output device, illustrating (in tabularform) load location and magnitude at different flexion angles, inaccordance with the disclosed embodiments;

FIG. 13 provides another exemplary screen shot of a user interface,which may be provided on a monitor or output device, illustrating (indiagrammatic form relative to the force sensing module) load locationand magnitude parameters in real-time, consistent with certain disclosedembodiments;

FIG. 14 provides an exemplary screen shot of a user interface, which maybe provided on a monitor or output device, illustrating (in diagrammaticform relative to the force sensing module) load location and magnitudeat predetermined flexion angles, in accordance with the disclosedembodiments;

FIG. 15 provides an exemplary screen shot of a user interface, which maybe provided on a monitor or output device, illustrating (in diagrammaticform relative to the force sensing module) current and historic loadlocation and magnitude parameters, consistent with certain disclosedembodiments; and

FIG. 16 provides an exemplary screen shot of a user interface, which maybe provided on a monitor or output device, providing exemplaryaggregated information on the relationship between load magnitude andlocation and overall patient satisfaction (as measurement by the WOMACindex), in accordance with the disclosed embodiments.

DETAILED DESCRIPTION

FIG. 1 provides a diagrammatic illustration of an exemplary kneebalancing system 100 for intra-operative detection, monitoring, andtracking of kinematic and/or kinetic parameters of an orthopedic joint,such as knee joint 120 of leg 110. For example, in accordance with theexemplary embodiment illustrated in FIG. 1, knee balancing system 100may embody a system for intra-operatively—and in real-time or nearreal-time—gathering, analyzing, and tracking performance parameters atknee joint 120 during a full or partial knee replacement procedure.Joint performance parameters may include or embody any parameter forcharacterizing the behavior or performance of an orthopedic joint.Non-limiting examples of joint performance parameters include anyinformation indicative of force, pressure, angle of flexion and/orextension, torque, varus/valgus displacement, location of center offorce, axis of rotation, relative rotation of tibia and femur, tibialcomponent rotation, range of motion, or orientation. Knee balancingsystem 100 may be configured to monitor one or more of these exemplarykinematic and/or kinetic parameters, track the kinematic and/or kineticparameters over time (and/or range of motion of the joint), and displaythe monitored and/or tracked data to a surgeon or medical professionalin real-time. As such, knee balancing system 100 provides a platformthat facilitates real-time intra-operative evaluation of several jointperformance parameters simultaneously.

As illustrated in FIG. 1, knee balancing system 100 may include a forcesensing module 130, one or more inertial measurement units 140 a, 140 b,a processing device (such as processing system 150 (or other computerdevice for processing data received by force sensing module 130)), andone or more wireless communication transceivers 160 for communicatingwith one or more of force sensing module 130 or one or more inertialmeasurement units 140 a, 140 b. The components of knee balancing system100 described above are exemplary only, and are not intended to belimiting. Indeed, it is contemplated that additional and/or differentcomponents may be included as part of knee balancing system 100 withoutdeparting from the scope of the present disclosure. For example,although wireless communication transceiver 160 is illustrated as beinga standalone device, it may be integrated within one or more othercomponents, such as processing system 150. Thus, the configuration andarrangement of components of force sensing system 100 illustrated inFIG. 1 are intended to be exemplary only. Individual components ofexemplary embodiments of force sensing system 100 will now be describedin more detail.

Processing system 150 may include or embody any suitablemicroprocessor-based device configured to process and/or analyzeinformation indicative of performance of the articular joint. Accordingto one embodiment, processing system 150 may be a general purposecomputer programmed for receiving, processing, and displayinginformation indicative of kinematic and/or kinetic parameters associatedwith the articular joint. According to other embodiments, processingsystem 150 may be a special-purpose computer, specifically designed tocommunicate with, and process information for, other componentsassociated with knee balancing system 100. Individual components of, andprocesses/methods performed by, processing system 150 will be discussedin more detail below.

Processing system 150 may be communicatively coupled to one or more offorce sensing module 130 and inertial measurement units 140 a, 140 b andconfigured to receive, process, and/or analyze data monitored by forcesensing module 130 and/or inertial measurement units 140 a, 140 b.According to one embodiment, processing system 150 may be wirelesslycoupled to each of force sensing module 130 and inertial measurementunits 140 a, 140 b via wireless communication transceiver(s) 160operating any suitable protocol for supporting wireless (e.g., wirelessUSB, ZigBee, Bluetooth, Wi-Fi, etc.) In accordance with anotherembodiment, processing system 150 may be wirelessly coupled to one offorce sensing module 130 or inertial measurement unit(s) 140 a, 140 b,which, in turn, may be configured to collect data from the otherconstituent sensors and deliver it to processing system 150.

Wireless communication transceiver(s) 160 may include any suitabledevice for supporting wireless communication between one or morecomponents of knee balancing system 100. As explained above, wirelesscommunication transceiver(s) 160 may be configured for operationaccording to any number of suitable protocols for supporting wireless,such as, for example, wireless USB, ZigBee, Bluetooth, Wi-Fi, or anyother suitable wireless communication protocol or standard. According toone embodiment, wireless communication transceiver 160 may embody astandalone communication module, separate from processing system 150. Assuch, wireless communication transceiver 160 may be electrically coupledto processing system 150 via USB or other data communication link andconfigured to deliver data received therein to processing system 150 forfurther processing/analysis. According to other embodiments, wirelesscommunication transceiver 160 may embody an integrated wirelesstransceiver chipset, such as the Bluetooth, Wi-Fi, NFC, or 802.11xwireless chipset included as part of processing system 150.

Force sensing module 130 may include a plurality of components that arecollectively adapted for implantation within at least a portion of anarticular joint and configured to detect various static and dynamicforces present at, on, and/or within the articular joint. According toone embodiment (and as shown in FIG. 1), force sensing module 130 mayembody a trial tibial implant prosthetic component configured forinsertion within a partially or fully resected and partially or fullyreconstructed knee joint 120. As will be explained in greater detailbelow, force sensing module 130 may be temporarily removably coupled toa tibial base component 121 b that is fitted to a resected portion oftibia 112 b via incision 122 through skin 111 of a patient's leg 110during a knee replacement procedure. Force sensing module 130 iscontoured to articulate with medial and lateral condyles of the femoralprosthetic component 121 b attached to a resected portion of thepatient's femur 112 a. Force sensing module 130 may also be contoured toarticulate with the un-resected natural knee of the patient. Once kneejoint 120 is fully or partially reconstructed, force sensing module 130may be configured to detect various kinematic and kinetic parameters atknee joint 120 in real-time, thereby allowing the surgeon theflexibility to make adjustments to the knee joint (e.g., by balancingthe tension of collateral ligaments 121 c, modifying the position and/ororientation of tibial or femoral prosthetic components 121 a, 121 b, or,if necessary, making adjustment to the bone cuts). Exemplary componentsand subsystems associated with force sensing module 130 will bedescribed in more detail below.

Inertial measurement unit(s) 140 a, 140 b may be any system suitable formeasuring information that can be used to accurately measure orientationin 3 dimensions. From this orientation information the joint angles suchas flexion and/or extension of the orthopedic joint can be derived.Joint flexion (and/or extension) data can be particular useful inevaluating the stability of the joint as the leg is flexed and extended.According to one embodiment, and as illustrated in FIG. 1, two inertialmeasurement units 140 a, 140 b are used and may be attached to the femurand tibia, respectively. Inertial measurements units have their ownreference coordinate frames and report their orientation with respect tothat frame. Inertial measurement units 140 a, 140 b are each configuredto measure the relative orientation of a bone with respect to areference orientation, such as the orientation of the respective sensorwhen the leg is positioned in a fully extended pose (0 degrees flexion)with no internal/external rotation or varus/valgus forces applied. Toimprove accuracy of the measurement, an initial calibration of theinertial measurement units with the units lying flat on the patient'stable at a known relative orientation may be performed prior toplacement on the patient's bones. A calibration fixture or jig thatunits can be temporarily and removably coupled to in a known relativeorientation that can be placed flat on the table surface may be utilizedfor this calibration. Alternatively or additionally, the inertialmeasurement units can be registered to anatomic axes of the femur andtibia using alignment guides/jigs and or using kinematic methods knownin the art. It should be noted that inertial measurement units 140 a,140 b can be attached to any feature of the patient's anatomy that willprovide information indicative of the flexion (and/or extension) of thejoint. For example, although FIG. 1 illustrates inertial measurementunits 140 a, 140 b as attached directly to femur 112 a and tibia 112 b,it is contemplated that additional reference attachments may be used.Indeed, according to one exemplary embodiment, one inertial measurementunit may be embedded within force sensing module 130 (which is affixedto the tibia via attachment to tibial prosthetic plate 121 b) and oneinertial measurement unit may be placed in a trial femoral prostheticcomponent 121 a (which is affixed to the femur). By affixing eachinertial measurement unit(s) 140 a, 140 b to different objects,measurement of the orientation of each object can be performed/obtainedindependently of the orientation or position of the other.

As illustrated in FIG. 1, the inertial measurement unit(s) 140 a, 140 bcan be fixed on the bones using pins, straps or any such means that canachieves a stable attachment. The actual location of the sensing modulerelative to the bone is not critical. From the orientation informationobtained from inertial measurement unit(s) 140 a, 140 b, thetibiofemoral flexion-extension, varus-valgus and rotation angles can becomputed. The range of these angles that the knee can traverse iscollectively referred to as knee range-of-motion (ROM). Exemplarycomponents and subsystems associated with force sensing module 130 willbe described in more detail with respect to FIG. 2.

FIG. 2 provides a magnified view of knee joint 120 showing force sensingmodule 130 coupled to tibial prosthetic component 121 b and configuredto articulate with femoral prosthetic component 121 a. In thisembodiment, force sensing module 130 is configured as a trial tibialimplant component that is to be used to monitor and evaluate thekinematic and/or kinetic performance of knee joint 120. For example,like a conventional trial tibial insert, an articular surface (i.e., thesurface that is configured to articulate with femoral prostheticcomponent 121 a) of force sensing module 130 may include a medialportion 330 a and a lateral portion 330 b that are contoured tocorrespond with the contoured shape of medial and lateral condyles offemoral prosthetic component 121 a. Unlike many conventional kneebalancing tools, force sensing module 130 is configured to replicate theshape, size and performance of the tibiofemoral interface with thepatella reduced, thereby insuring more accurate kinematic and/or kineticmeasurement results and more reliable prediction of post-operative jointperformance.

FIG. 3 provides a schematic diagram illustrating certain exemplarysubsystems associated with force sensing system 100 and its constituentcomponents. Specifically, FIG. 3 is a schematic block diagram depictingexemplary subcomponents of processing system 150, force sensing module130, and inertial measurement unit(s) 140 a, 140 b in accordance withcertain disclosed embodiments.

As explained, processing system 150 may be any processor-based computingsystem that is configured to receive kinematic and/or kinetic parametersassociated with an orthopedic joint 120, analyze the received parametersto extract data indicative of the performance of orthopedic joint 120,and output the extracted data in real-time or near real-time.Non-limiting examples of processing system 150 include a desktop ornotebook computer, a tablet device, a smartphone, or any other suitableprocessor-based computing system.

For example, as illustrated in FIG. 3, processing system 150 may includeone or more hardware and/or software components configured to executesoftware programs, such as software tracking kinematic and/or kineticparameters associated with orthopedic joint 120 and displayinginformation indicative of the kinematic and/or kinetic performance ofthe joint. According to one embodiment, processing system 150 mayinclude one or more hardware components such as, for example, a centralprocessing unit (CPU) 251, a random access memory (RAM) module 252, aread-only memory (ROM) module 253, a memory or data storage module 254,a database 255, one or more input/output (I/O) devices 256, and aninterface 257. Alternatively and/or additionally, processing system 150may include one or more software media components such as, for example,a computer-readable medium including computer-executable instructionsfor performing methods consistent with certain disclosed embodiments. Itis contemplated that one or more of the hardware components listed abovemay be implemented using software. For example, storage 254 may includea software partition associated with one or more other hardwarecomponents of system 150. Processing system 150 may include additional,fewer, and/or different components than those listed above. It isunderstood that the components listed above are exemplary only and notintended to be limiting.

CPU 251 may include one or more processors, each configured to executeinstructions and process data to perform one or more functionsassociated with processing system 150. As illustrated in FIG. 3, CPU 251may be communicatively coupled to RAM 252, ROM 253, storage 254,database 255, I/O devices 256, and interface 257. CPU 251 may beconfigured to execute sequences of computer program instructions toperform various processes, which will be described in detail below. Thecomputer program instructions may be loaded into RAM 252 for executionby CPU 251.

RAM 252 and ROM 253 may each include one or more devices for storinginformation associated with an operation of processing system 150 and/orCPU 251. For example, ROM 253 may include a memory device configured toaccess information associated with processing system 150, includinginformation for identifying, initializing, and monitoring the operationof one or more components and subsystems of processing system 150. RAM252 may include a memory device for storing data associated with one ormore operations of CPU 251. For example, ROM 253 may load instructionsinto RAM 252 for execution by CPU 251.

Storage 254 may include any type of mass storage device configured tostore information that CPU 251 may need to perform processes consistentwith the disclosed embodiments. For example, storage 254 may include oneor more magnetic and/or optical disk devices, such as hard drives,CD-ROMs, DVD-ROMs, or any other type of mass media device. Alternativelyor additionally, storage 254 may include flash memory mass media storageor other semiconductor-based storage medium.

Database 255 may include one or more software and/or hardware componentsthat cooperate to store, organize, sort, filter, and/or arrange dataused by processing system 150 and/or CPU 251. For example, database 255may include historical data such as, for example, stored kinematicand/or kinetic performance data associated with the orthopedic joint.CPU 251 may access the information stored in database 255 to provide aperformance comparison between previous joint performance and current(i.e., real-time) performance data. CPU 251 may also analyze current andprevious kinematic and/or kinetic parameters to identify trends inhistorical data (i.e., the forces detected at medial and lateralarticular surfaces at various stages of ligament release or boneresection. These trends may then be recorded and analyzed to allow thesurgeon or other medical professional to compare the data at variousstages of the knee replacement procedure. It is contemplated thatdatabase 255 may store additional and/or different information than thatlisted above.

I/O devices 256 may include one or more components configured tocommunicate information with a user associated with force sensing system100. For example, I/O devices may include a console with an integratedkeyboard and mouse to allow a user to input parameters associated withprocessing system 150. I/O devices 256 may also include a displayincluding a graphical user interface (GUI) (such as GUI 900 shown inFIG. 9) for outputting information on a display monitor 258 a. I/Odevices 256 may also include peripheral devices such as, for example, aprinter 258 b for printing information associated with processing system150, a user-accessible disk drive (e.g., a USB port, a floppy, CD-ROM,or DVD-ROM drive, etc.) to allow a user to input data stored on aportable media device, a microphone, a speaker system, or any othersuitable type of interface device.

Interface 257 may include one or more components configured to transmitand receive data via a communication network, such as the Internet, alocal area network, a workstation peer-to-peer network, a direct linknetwork, a wireless network, or any other suitable communicationplatform. For example, interface 257 may include one or more modulators,demodulators, multiplexers, demultiplexers, network communicationdevices, wireless devices, antennas, modems, and any other type ofdevice configured to enable data communication via a communicationnetwork. According to one embodiment, interface 257 may be coupled to orinclude wireless communication devices, such as a module or modulesconfigured to transmit information wirelessly using Wi-Fi or Bluetoothwireless protocols. Alternatively or additionally, interface 257 may beconfigured for coupling to one or more peripheral communication devices,such as wireless communication transceiver 160.

As explained, inertial measurement unit(s) 140 a, 140 b may include oneor more subcomponents configured to detect and transmit information thateither represents a 3-dimensional orientation or can be used to derivean orientation of the inertial measurement unit 140 a, 140 b (and, byextension, any object rigidly affixed to inertial measurement unit 140a, 140 b, such as a tibia and femur of a patient). Inertial measurementunit(s) 140 a, 140 b may embody a device capable of determining a3-dimensional orientation associated with any body to which inertialmeasurement unit(s) 140 a, 140 b is/are attached. According to oneembodiment, inertial measurement unit(s) 140 a, 140 b may include acontroller 241, a power supply 242, and one or more of a gyroscope 243,one or more of an accelerometer 244, or one or more of a magnetometer245, signal conditioning circuitry 246, and interface 248. Optionally. atemperature sensor may also be included (not shown) to compensate forthe effect of temperature on sensor readings.

Although FIG. 3 illustrates inertial measurement unit(s) 140 a, 140 b ascontaining 3-axis gyroscope 243, 3-axis accelerometer 244, and 3-axismagnetometer 245, fewer of these devices with fewer axes can be usedwithout departing from the scope of the present disclosure. For example,according to one embodiment, inertial measurement units may include onlya gyroscope and an accelerometer, the gyroscope for calculating theorientation based on the rate of rotation of the device, and theaccelerometer for measuring earth's gravity and linear motion, theaccelerometer providing corrections to the rate of rotation information(based on errors introduced into the gyroscope because of devicemovements that are not rotational or errors due to biases and drifts).In other words, the accelerometer may be used to correct the orientationinformation collected by the gyroscope. Similar the magnetometer 245 canbe utilized to measure the earth's magnetic field and can be utilized tofurther correct gyroscope errors. Thus, while all three of gyroscope243, accelerometer 244, and magnetometer 245 may be used, orientationmeasurements may be obtained using as few as one of these devices. Theuse of additional devices increases the resolution and accuracy of theorientation information and, therefore, may be preferable in embodimentswhere resolution is critical.

Controller 241 may be configured to control and receive conditioned andprocessed data from one or more of gyroscope 243, accelerometer 244, andmagnetometer 245 and transmit the received data to one or more remotereceivers. The data may be pre-conditioned via signal conditioningcircuitry 246 consisting of amplifiers and analog-to-digital convertersor any such circuits. The signals may be further processed by a motionprocessor 247. Motion processor 247 may be programmed with “motionfusion” algorithms to collect and process data from different sensors togenerate error corrected orientation information. Accordingly,controller 241 may be communicatively coupled (e.g., wirelessly viainterface 248 as shown in FIG. 3, or using a wireline protocol) to, forexample, processing system 150 and configured to transmit theorientation data received from one or more of gyroscope 243,accelerometer 244, and magnetometer 245 to processing system 150, forfurther analysis. Interface 248 may include one or more componentsconfigured to transmit and receive data via a communication network,such as the Internet, a local area network, a workstation peer-to-peernetwork, a direct link network, a wireless network, or any othersuitable communication platform. For example, interface 248 may includeone or more modulators, demodulators, multiplexers, demultiplexers,network communication devices, wireless devices, antennas, modems, andany other type of device configured to enable data communication via acommunication network. According to one embodiment, interface 248 may becoupled to or include wireless communication devices, such as a moduleor modules configured to transmit information wirelessly using Wi-Fi orBluetooth wireless protocols. As illustrated in FIG. 3, inertialmeasurement unit(s) 140 a, 140 b may be powered by power supply 242,such as a battery, fuel cell, MEMs micro-generator, or any othersuitable compact power supply.

Force sensing module 130 may include a plurality of subcomponents thatcooperate to detect force data and, in certain embodiments, joint and/ortibial component orientation information at orthopedic joint 120, andtransmit the detected data to processing system 150, for furtheranalysis. According to one exemplary embodiment, force sensing module130 may include a controller 231, a power supply 232, an interface 235,and one or more force sensors 233 a, 233 b, . . . , 233 n coupled tosignal conditioning circuits 234. Those skilled in the art willrecognize that the listing of components of force sensing module 130 isexemplary only and not intended to be limiting. Indeed, it iscontemplated that force sensing module 130 may include additional and/ordifferent components than those shown in FIG. 3. For example, althoughFIG. 3 illustrates controller 231, signal conditioning 234, andinterface 235 as separate components, it is contemplated that thesecomponents may embody one or more modules (either distributed orintegrated) within a microprocessor 230. Alternatively or additionally,force sensing module 130 may include one or more integrated inertialmeasurement units (e.g., motion sensors, orientation sensors, etc.) fordetermining the orientation of force sensing module 130. Exemplarysubcomponents of force sensing module 130 will be described in greaterdetail below with respect to FIG. 4.

FIG. 4 illustrates an exploded perspective view of force sensing module130, consistent with certain disclosed embodiments. As illustrated inFIG. 4, force sensing module 130 may include a housing having an upperportion 430 a and a lower portion 430 b. As explained, upper portion 430a may comprise an articular surface that includes medial portion 330 aand lateral portion 330 b, each of which is contoured to interact withrespective medial and lateral condyles of a femoral prosthetic component112 a or the condyles of a natural un-resected femur. Lower portion 430b may comprise a bottom surface comprising an interconnect element 430c, configured to removably and slideably couple force sensing module toa metallic tray associated with the tibial prosthetic component 121 b.Lower portion 430 b of housing may also comprise a tray 430 d forreceiving and laterally securing a battery (not shown) within housing offorce sensing module 130. Upper portion 430 a and lower portion 430 bmay be configured to interlock with one another in order to provide asubstantially water-tight containment vessel for the electroniccomponents of force sensing module 130.

Force sensing module 130 may include an electronic circuit board 431,such as printed circuit board (PCB), multi-chip module (MCM), or flexcircuit board, configured to provide both integrated, space-efficientelectronic packaging and mechanical support for the various electricalcomponents and subsystems of force sensing module 130. Force sensingmodule 130 may also include controller 231 and interface 234 (shown asmicrocontroller system-on-chip with integrated RF transceiver 444 inFIG. 4), a first set of force sensors 432 a-432 c associated with medialportion 330 a of force sensing module 130, a second set of force sensors433 a-433 c associated with lateral portion 330 b of force sensingmodule 130, a power supply (not shown in FIG. 4, but shown as powersupply 232 of FIG. 3), signal conditioning circuitry 234, and(optionally) one or more inertial measurement units 445 for detectingthe orientation of force sensing module 130 relative to a referenceposition.

Microcontroller 444 (and/or controller 231 and interface 235) may beconfigured to receive data from one or more of force sensors 423 a-432c, 433 a-433 c and inertial measurement unit 445, and transmit thereceived data to one or more remote receivers. The data may bepre-conditioned via signal conditioning circuitry 246 consisting ofamplifiers and analog-to-digital converters or any such circuits. Thesignal conditioning circuitry may also be used to condition the powersupply voltage levels to provide a stable reference voltage foroperation of the sensors. Accordingly, microcontroller 444 may include(or otherwise be coupled to) an interface 235 that may consist of awireless transceiver chipset with or without an external antenna, andmay be configured for communicative coupling (e.g., wirelessly as shownin FIG. 3, or using a wireline protocol) to, for example, processingsystem 150. As such, microcontroller 444 may be configured to transmitthe detected force and orientation data received from one or more ofsensors 423 a-432 c, 433 a-433 c, and inertial measurement unit 445 toprocessing system 150, for further analysis. Interface 235 may includeone or more components configured to transmit and receive data via acommunication network, such as the Internet, a local area network, aworkstation peer-to-peer network, a direct link network, a wirelessnetwork, or any other suitable communication platform. For example,interface 235 may include one or more modulators, demodulators,multiplexers, demultiplexers, network communication devices, wirelessdevices, antennas, modems, and any other type of device configured toenable data communication via a communication network. According to oneembodiment, interface 235 may be coupled to or include wirelesscommunication devices, such as a module or modules configured totransmit information wirelessly using Wi-Fi or Bluetooth wirelessprotocols. As illustrated in FIG. 3, force sensing module 130 may bepowered by power supply 232, such as a battery, fuel cell, MEMsmicro-generator, or any other suitable compact power supply.

Force sensing module 130 may optionally include an inertial measurementunit 445 to provide orientation (and/or position) information associatedwith force sensing module 130 relative to a reference orientation(and/or position). Inertial measurement unit 445 may include one or moresubcomponents configured to detect and transmit information that eitherrepresents an orientation or can be used to derive an orientation of theinertial measurement unit 445 (and, by extension, any object that isrigidly affixed to inertial measurement unit 445, such as a tibialcomponent which is further attached to the tibia of the patient).Inertial measurement unit 445 may embody a device capable of determininga 3-dimensional orientation associated with any body to which inertialmeasurement unit 445 is attached. According to one embodiment, inertialmeasurement unit 445 may include one or more of a gyroscope 243, anaccelerometer 244, or a magnetometer 245, signal conditioning circuitry246, and interface 248.

As illustrated in FIGS. 3 and 4, force sensing module 130 may include aplurality of force sensors, each configured to measure respective forceacting on the sensor. The type and number of force sensors providedwithin force sensing module 130 can vary depending upon the resolutionand the desired amount of data. For example, one sensor could be used ifthe design goal of force sensing system 130 is to simply detect themagnitude of force present at the tibiofemoral interface. If, however,the design goal of force sensing system 130 is to not only provide themagnitude of the forces present at the tibiofemoral interface, but alsoestimate the location of the center of the applied force, thenadditional sensors (as few as two, but, preferably, at least three)should be used to provide a sufficient number of data points to allowfor accurate planar triangulation of the location of the center of thedetected force. Furthermore, in embodiments where the design goal offorce sensing system 130 is to provide independent (and simultaneous)monitoring of forces (both magnitude and location of center of force)applied at medial and lateral regions of the articular surface, thenforce sensing system 130 should include as few as four force sensors(two for each of medial and lateral portions 330 a, 330 b,respectively), but, preferably, at least six force sensors (three foreach of the medial and lateral portions, 330 a, 330 b, respectively).

As illustrated in FIG. 4, force sensing module 130 may include a firstset of force sensors 432 a-432 c and a second set of force sensors 433a-433 c. According to one embodiment, the first set 432 a-432 c may bemechanically coupled to the underside of medial portion 330 a ofarticular surface of housing 430 a. Similarly, the second set 433 a-433c may be mechanically coupled to the underside of lateral portion 330 bof articular surface of housing 430 a. As such, the first set of forcesensors 432 a-432 c may be configured to detect forces incident onmedial portion 330 a of articular surface, while the second set of forcesensor 433 a-433 c may be configured to detect forces incident onlateral portions 330 b of articular surface.

According to certain embodiments consistent with the present disclosure,medial portion 330 a and lateral portion 330 b are substantiallymechanically isolated from one another. As such, forces incident uponmedial portion 330 a are not meaningfully detectable by a second set offorce sensors 433 a-433 c. Similarly, this substantial mechanicalisolation ensures that forces incident upon lateral portion 330 b arenot meaningfully detectable (e.g., they may appear as noise orinterference) by first set of force sensors 432 a-432 b. It should benoted that substantial mechanical isolation, as the term is used herein,should not be so limited as to require no mechanical interaction betweenmedial portion 330 a and lateral portion 330 b.

There are multiple ways in which mechanical isolation between medialportions 330 a and lateral portions 330 b may be achieved. According toone embodiment, the upper portion 430 a of housing may embody athree-piece assembly in which medial and lateral portions 330 a, 330 bare mechanically separate components so as to physically isolatecompressive forces on the medial and lateral sides from each other andfrom the housing side walls and other support structures. In such aconfiguration, medial portion 330 a of articular surface is suspendedabove force sensors 432 a-432 c and is free to move by a small butadequate amount relative to the housing in the downward direction whensubjected to compressive forces. Similarly, lateral portion 330 b ofarticular surface is suspended above force sensors 433 a-433 c and isfree to move by a small but adequate amount relative to the housing inthe downward direction when subjected to compressive forces. The piecescan be securely sealed to the housing with a thin layer of siliconesealant or a gasket of a soft, deformable material like rubber.

According to another embodiment, upper portion 430 a of housing mayembody a single piece of material in which medial and lateral portions330 a, 300 b are constructed to be significantly thinner (and lessmechanically resistant to deformation) than the rest of the enclosure,allowing them to flex under compressive loads and transfer the majorityof the forces to first and second sets of force sensors 432 a-432 c, 433a-433 c, respectively. In this embodiment, the medialateral bridgeseparating medial portion 330 a and lateral portion 330 b, as well asthe support structure surrounding the perimeter of upper portion 430 aof housing may comprise a substantially thicker and more rigid (and moremechanically resistance to deformation), thereby substantiallymechanically isolating medial portion 330 a from lateral portion 330 b.Exemplary functional subcomponents of force sensors 432 a-432 c and 433a-433 c will now be described in greater detail below with respect toFIGS. 5A-5C.

Force sensors 432 a-432 c and 433 a-433 c may be configured using avariety of different resistive or capacitive strain gauges for detectingapplied force and/or pressure. Force sensors 432 a-432 c and 433 a-433 ceach comprise two primary components: a metric portion that has aprescribed mechanical force-to-deflection characteristic and a measuringportion for accurately measuring the deflection of the metric portionand converting this measurement into an electrical output signal (using,for example, strain gauges). Each of FIG. 5A illustrates differentdesigns for the metric portion of the force.

Specifically, FIG. 5A illustrates different designs, each of which ispredicated on a different mechanical deformation principle, and any ofwhich may be used in different exemplary embodiments. For example, forcesensors 432 a-432 c and 433 a-433 c may embody at least one type of thefollowing configurations of force sensors: binocular 533 a, ring 533 b,shear 533 c, or direct stress or spring torsion 533 d (includinghelical, disc, etc.) The strain gauges used with any of the aboveconfigurations can be either resistive, piezoresistive, capacitive,optical, magnetic or any such transducers that convert a mechanicaldeflection and/or strain to a measurable electrical parameter.Alternatively or additionally, any suitable resistive strain gauge,whose output resistance value changes with respect to the application ofmechanical force, can be used as force sensors 432 a-432 c, 433 a-433 c.In certain embodiments, the resistive strain gauge could be thetransducer class S182K series strain gauges from Vishay Precision Group,Wendell N.C. In another embodiment, as shown in FIG. 4, force sensors432 a-432 c and 433 a-433 c are load cells that combine the metric andmeasuring portion as a single package, such as the LBS miniaturecompression load button manufactured by Interface of Scottsdale Ariz. orLLB130 Subminiature Load Button manufactured by Futek of Irvine, Calif.can be used. Such load cells have wired connections that can be directlysoldered on to the printed circuit board.

Because the structures used in resistive sensors tend to exhibitrelatively small changes in resistance under mechanical stress, aseparate electrical circuit that is capable of detecting such smallchanges may be required. According to one embodiment, a Wheatstonebridge circuit 540 may be used to measure the static or dynamicelectrical resistance due to small changes in resistance due tomechanical strain.

As an alternative or in addition to resistive strain gauges, forcesensors 432 a-432 c and 433 a-433 c may embody capacitive-type straingauges. Capacitive-type strain gauges, such as those illustrated in theembodiments shown in FIGS. 5B and 5C, typically comprise two metalconductors fashioned as layers or plates separated by a dielectriclayer. The dielectric layer may comprise a compressible material, suchthat when force is applied to one or more of the metal plates thedielectric layer compresses and changes the distance between the metalplates. This change in distance causes a change in the capacitance,which can be electrically measured and converted into a force value.

Exemplary designs of capacitive-type force sensors are illustrated inFIGS. 5B and 5C. For example, FIG. 5B illustrates capacitive-type sensor550 with a lateral comb configuration (i.e., having a serpentinedielectric channel 550 c separating metal plates 550 a and 550 b).Because this lateral-comb configuration effectively comprises severalcapacitors (at each of the interlocking comb-teeth), a lateral combcapacitive sensor 550 functions across a relatively large range offorces and exhibits good sensitivity and signal to noise ratio.

According to another exemplary embodiment, capacitive-type force sensormay embody a more conventional parallel-plate capacitor device 555, withmetal plates 555 a and 555 b arranged in parallel around a dielectriclayer 555 c. Although less sensitive to compressive forces, parallelplate designs are simpler and less expensive to implement, and can befairly accurate over smaller ranges of compressive forces.

FIG. 6 provides a perspective exploded view of an alternate design offorce sensing module 130. In the embodiment illustrated in FIG. 6,medial portion 330 a and lateral portion 330 b are not integrated aspart of upper portion 430 a of the housing. Having physically separatemedial and lateral portions 330 a, 330 b provides better mechanicalisolation between medial and lateral portions 330 a, 330 b, ensuring agreater degree of independence between medial and lateral forcemeasurements.

Force sensing module 130 illustrated in FIG. 6 may comprise a medialforce sensing device 640 a and a lateral force sensing device 640 b.Unlike the embodiment of force sensing device 130 illustrated in FIG. 4,each of medial and lateral force sensing device 640 a, 640 b of forcesensing module 130 of FIG. 6 embodies a single force sensing structurethat includes a plurality of transducer elements 641 a-641 f. Each oftransducer elements 641 a-641 f is configured to independently detect aforce value associated with a force incident on a respective location oneither the medial portion 330 a or the lateral portion 330 b of thearticular surface of the housing. The configuration of medial andlateral force sensing devices 640 a, 640 b will be discussed in furtherdetail below with respect to FIGS. 7A-7E.

As with the embodiment of the force sensing module illustrated in FIG.4, force sensing module 130 of FIG. 6 may include an electronic circuitboard 631, the components of which have not been illustrated in detail.Nevertheless, electronic circuit board 631 may comprise a printedcircuit board (PCB), multi-chip module (MCM), or flex circuit board,configured to provide both integrated, space-efficient electronicpackaging and mechanical support for the various electrical componentsand subsystems of force sensing module 130. Electronic circuit board 631may also include a microcontroller (with communication interface module)(not shown in FIG. 6, but similar to that shown in FIG. 4), a powersupply (not shown in FIG. 6, but similar to power supply 232 of FIG. 3),signal conditioning circuits (not shown in FIG. 6, but similar to signalconditioning circuit 234 of FIG. 3), and (optionally) one or moreinertial measurement units (similar to that disclosed and illustratedwith respect to FIG. 4) for detecting the orientation of force sensingmodule 130 relative to a reference position. Electronic circuit board631 may also include a plurality of electrical interconnects to connectforce sensing devices 640 a, 640 b and other components to themicrocontroller other electronic components of electronic circuit board631.

FIGS. 7A-7E each provide a different view of exemplary force sensingdevices 640 a, 640 b used in the embodiment of force sensing module 130illustrated in FIG. 6. Specifically, FIG. 7A illustrates a perspectivetop view, FIG. 7B illustrates and overhead top view, FIG. 7C illustratesa cross section view of the cantilever-type mechanical structure offorce sensing devices 640 a, 640 b, FIG. 7D illustrates a side view ofinverted force sensing devices 640 a, 640 b, and FIG. 7E illustrates afront view.

As shown in FIG. 7A, each of force sensing modules 640 a, 640 b mayinclude a plurality of transducers (each embodying an individual loadsensing element). Each transducer includes a respective cantilevercomponent 641, one or more respective strain gauges 642, and a contactpoint. At least a portion of the cantilever component 641 is configuredto deform in response to the first force incident upon the articularsurface. Each cantilever has a well-defined contact point that isconfigured to interact with a corresponding contact point located on theunderside of respective medial or lateral portion 330 a, 330 b of thearticular surface of the housing. According to the exemplary embodimentof FIG. 7A, this contact point may embody a plastic circular nipple(shown in FIG. 7A as the hemispheric structure located toward the distalend of the cantilever structure). This hemispheric structure may beconfigured to contact a complementary structure located on the undersideof a corresponding medial or lateral portion 330 a, 330 b of articularsurface, such that, when a load is applied to the corresponding medialor lateral portion 330 a, 330 b, the force is mechanically translatedonto cantilever beam, forcing the cantilever beam to mechanically deformconsistent with the magnitude of the load applied at that particularlocation of medial or lateral portion 330 a, 330 b.

As explained, each of transducers of force sensing modules 640 a, 640 bmay also include one or more respective strain gauges 642. Strain gauge642 may be coupled to a respective cantilever component 641 andconfigured to measure the deformation in the respective cantilevercomponent. Strain gauge 642 may embody resistive strain gauges, meaningthat it exhibits a change in resistance in response to the pressuredetected at the corresponding cantilever component 641. According to oneembodiment, strain gauges 641 may be the Transducer-Class strain gaugesmanufactured by Micro-Measurement (Wendell, N.C.).

As illustrated in the embodiment shown in FIGS. 7A-7E, force sensingmodules 640 a, 640 b may include three cantilever elements, extendinglaterally from a central base support element. Each cantilever component641 associated with the plurality of transducers is vertically supportedat a proximal end by a common central base component. Those skilled inthe art will recognize that additional or fewer cantilever components641 may be included as part of force sensing modules 640 a, 640 b.Additionally, the base support element may be a single support elementshared by sensing module 640 a, 640 b, and may be large enough to havelateral dimensions roughly equal to the lateral dimensions of the bottompiece of the housing 430 b. In the exemplary embodiment illustrated inFIGS. 7A-7E, three cantilever components are used to provide a balancebetween cost and precision of the force locating capability of forcesensing modules 640 a, 640 b versus load cells provided by vendors asshown in the embodiment of FIG. 4.

FIG. 8 illustrates an alternate knee balancing configuration, consistentwith the disclosed embodiments. Specifically, FIG. 8 illustrates a gapmeasurement module 800, that can be used to determine the gap distancebetween two surfaces located at the joint interface (e.g., as at theinterface between the tibia and femur). As illustrated in FIG. 8, gapmeasurement module 800 may include a plurality of springs (such asmedial spring 820 a and lateral spring 820 b) configured to changelength in response to compressive forces at the tibiofemoral interface.In operation, biasing the springs on the medial and lateral sides canchange the thickness of the sensing module dynamically.

Various spring designs can be employed such as, for example and withoutlimitation, helical compression springs, constant force springs,cantilever springs, etc. In certain embodiments, a screw can also beemployed to enable adjustment in tension and thereby vary the forcesexperienced by the medial and lateral sides. In a further exemplaryaspect, the amount of tension of each spring could be confirmed withmeasurements made by integrated force sensors similar to embodimentsillustrated in FIG. 4 and FIG. 6. One skilled in the art will appreciatethat, once the forces are equalized, the gap measurements can beemployed to perform “gap balancing”, one of the techniques utilized forligament balance.

In other aspects, a plurality of linear displacement or distance sensors830 a, 830 b can also be incorporated in the housing, and can beconfigured to determine the distance between the top and bottom of thehousing dynamically. In this aspect, distance sensors 830 a, 830 b eachcomprise a transducer operable to convert linear displacement to anelectrical signal that can then be processed and transmitted wirelessly.Such a transducer could be, for example and without limitation, optical,inductive, electromagnetic, resistive or the like. In another aspect,the device disclosed in U.S. Pat. No. 8,026,729 filed on Apr. 1, 2009,hereby incorporated by reference, can be particularly suited.

Gap measurement module 800 may include an electronic circuit board 810that includes a microcontroller configured to receive data from distancesensors 830 a, 830 b and wirelessly communicate the received informationto an off-board monitoring system, such as processing system 150.

According to one embodiment, gap measurement module 800 may include aplastic or silicon housing with flexible sides to accommodate the changein vertical dimensions. This flexible housing may embody a bellows oraccordion type housing or thinner housing walls compared to the housingtop and bottom can be used to allow for changes in vertical dimensions.

As explained, force sensing module 130 may be configured to be removablypositioned within the articular joint 120 in a variety of ways. Forexample, force sensing module 130 may be slideably coupled to a tibialprosthetic plate 121 b during extended periods of joint evaluation. Insome situations, however, it may be impractical to couple force sensingmodule 130 to the tibial plate. For example, when a surgeon isreasonably certain that additional bone cuts or prosthetic componentrepositioning may be required, it may be time consuming and inconvenientto have to frequently couple and remove force sensing module 130 to andfrom tibial prosthetic plate 121 b. In such situations, it may beadvantageous to have a system for quickly (and temporarily) positioningforce sensing module 130 at or within articular joint 120. Anotherexample is when a surgeon has only made a tibial cut and wishes toassess joint performance with an un-resected or partially resectedfemur. In this situation, there may not be enough room for a tibialprosthetic plate 121 b or it not may not be practical and/or useful froma work flow or clinical perspective to utilize a tibial plate. FIG. 9illustrates one embodiment of an elongated handle member 930 configuredto removably position the force sensing module 130 within the orthopedicarticular joint 120.

As illustrated in FIG. 9, elongated handle member 930 may include achannel that complimentarily corresponds to slideable connectioninterface 430 a of force sensing module 130. As such, elongated handlemember 930 can be slideably coupled to force sensing module 130 and usedin situations in which the force sensing module 130 need to berepositioned within the orthopedic joint 120 on a more frequent basis.

Processes and methods consistent with the disclosed embodiments providea system for monitoring the forces (or gaps) present at an orthopedicjoint 120 and the 3-dimensional alignment and/or angles of the joint,and can be particularly useful in intra-operatively evaluating thekinematic and/or kinetic performance of the joint. As explained, whilevarious components, such as force sensing module 130 and inertialmeasurement units 140 a, 140 b can monitor various physical parameters(e.g., magnitude and location of force, orientation, etc.) associatedwith the bones and interfaces that make up orthopedic joint 130,processing system 150 provides a centralized platform for collecting andcompiling the various physical parameters monitored by the individualsensing units of the system, analyzing the collected data, andpresenting the collected data in a meaningful way to the surgeon. FIGS.10, 10A, and 11 illustrate exemplary processes and features associatedwith how processing system 150 performs the data analysis andpresentation functions associated with force sensing system 100.

FIGS. 10 and 10A provide exemplary screen shots 900, 970 correspondingto a graphical user interface (GUI) associated with processing system150. Screen shot 900 may correspond to embodiments in which forcesensing module 130 is configured to detect forces present at orthopedicjoint 120. Screen shot 970 may correspond to embodiments in which gapmeasurement module 800 is configured to detect a gap distance at thetibiofemoral interface. Specific details for each of these screen shotswill be described in detail below with respect to the exemplaryprocesses and methods performed by processing system 150, as outlined inFIG. 11.

FIG. 11 provides a flowchart illustrating an exemplary data analysisprocess 1000 performed by processing system 150. As explained,processing system 150 may include software configured to receive,process, and deliver various kinematic and/or kinetic performance datato other subcomponents and users associated with force sensing system100.

As illustrated in FIG. 11, the process may commence when processingsystem 150 receives force measurement information from force sensingmodule 130 (or gap measurement information from gap measurement module800) (Step 1002) and/or orientation information from inertialmeasurement unit(s) 140 a, 140 b (Step 1004). As explained, processingsystem 150 may include one or more communication modules for wirelesslycommunicating data with force sensing module 130 (or gap measurementmodule 800) and/or inertial measurement unit(s) 140 a, 140 b. As such,processing system 150 may be configured establish a continuouscommunication channel with force sensing module 130 and/or inertialmeasurement unit(s) 140 a, 140 b and automatically receive kinematicand/or kinetic data across the channel. Alternatively or additionally,processing system 150 may send periodic requests to one or more of forcesensing module 130 and/or inertial measurement unit(s) 140 a, 140 b andreceive updated kinematic and/or kinetic parameters in response to therequests. In either case, processing system 150 receives force andorientation information in real-time or near real-time.

Processing system 150 may be configured to determine a magnitude and/orlocation of the center of the force detected by force sensing module 130(Step 1012). In certain embodiments, force sensing module 1340 may beconfigured to determine the location of the center of the force relativeto the boundaries of the articular surface. In such embodiments,processing system 150 may not necessarily need to determine thelocation, since the determination was made by force sensing module 130.

In other embodiments, processing system 150 simply receives raw forceinformation (i.e., a point-force value) from each sensor of forcesensing module 130, along with data identifying which force sensordetected the particular force information. In such embodiments,processing system 150 may be configured to determine the location of thecenter of the force, by triangulating the center based on the relativevalue of a magnitude and the position of the force sensor within theforce sensing module 130.

Processing system 150 may also be configured to determine an angle offlexion/extension of joint 120 based on the orientation informationreceived from inertial measurement unit(s) 140 a, 140 b (Step 1014). Forexample, processing system 150 may be configured to receivepre-processed and error-corrected orientation information from theinertial measurement unit(s) 140 a, 140 b. Alternatively, processingsystem 150 may be configured to receive raw data from one or more ofgyroscope 243, accelerometer 244, and/or magnetometer 245 and derive theorientation based on the received information using known processes fordetermining orientation based on rotation rate data from gyroscope,acceleration information from accelerometer, and magnetic fieldinformation from magnetometer. In order to enhance precision of theorientation information, data from multiple units may be used to correctdata from any one of the units. For example, accelerometer and/ormagnetometer data may be used to correct error in rotation rateinformation due to gyroscope bias and drift issues. Optional temperaturesensor information may also be utilized to correct for temperatureeffects.

Once processing system 150 has determined the magnitude and location ofthe center of the force detected the force sensors and jointflexion/extension, varus/valgus, and internal/external rotation anglesprocessing system 150 may analyze and compile the data for presentationin various formats that may be useful to a user of force sensing system100 (Step 1022). For example, as shown in FIG. 10, processing system 150may be configured to display the instantaneous magnitude and location ofthe center of the force (display area 940) on a portion of the GUI 900.According to one embodiment, software associated with processing system150 may provide graphs 940 a, 940 b indicating the relative magnitude ofthe center of force detected at the respective sensors associated withmedial and lateral portions 330 a, 330 b of the articular surface. Ascan be seen in FIG. 10, graphs 940 a, 940 b may include vertical gaugesindicating the various force values that are detectable by processingsystem 150, along with a horizontal line that shows the instantaneousmagnitude of the force value with respect to the gauge of possiblevalues. As an alternative or in addition to graphs 940 a, 940 b,processing system 150 may be configured to simply display the numericalvalue of the medial and lateral forces, as shown in user interfaceelements 942 a, 942 b.

In addition to magnitude values, processing system 150 may include auser interface element configured to display the instantaneous locations941 a, 941 b of the center of the medial and lateral forces relative tothe boundaries of the articular surface. In addition to the location,the graphical element may also be configured to adjust the size of thecursor or icon used to convey the location information to indicate therelative magnitude of the force value. It should be noted that variousother information can be provided as a user interface element associatedwith GUI 900.

For example, as an alternative or in addition to the magnitude and forcepresentation described above with respect to user interface region 940,processing system 150 may include user interface elements 950 a, 950 b,950 c that provides information indicative of the instantaneous valuesfor flexion/extension (950 b), internal/external rotation (950 a), andvarus/valgus alignment (950 c), each of which processing system 150 candetermine based on the 3-dimensional orientation information frominertial measurement unit(s) 140 a, 140 b (Step 1024). As part of thisdisplay element, processing system may also display graphicalrepresentations of femur 912 a, tibia 912 b, and force sensing module930, based on the instantaneous position data received from inertialmeasurement unit(s) 140 a, 140 b. The graphical representation mayconsist of an artificial model of the knee representing an approximationof the patient's knee, animated in real-time as the joint angles changein response to articulation of the joint by the surgeon. Alternatively,in the case where 3D image of the patient's joint is available, ananatomically correct 3D model of the patient's knee may be created bythe processing unit 150 and animated in real-time.

According to an exemplary embodiment, processing system 150 may also beconfigured to generate a user interface element 960 that displays datathat tracks the magnitude (y-axis, 960 b) medial and lateral forcevalues 961 a, 961 b as a function of flexion/extension angle (x-axis,960 a) (Step 1026). User interface element 960 may provide bothinstantaneous and historical medial and lateral force magnitude data 960a as a function of flexion/extension angle 960 a. This may beparticularly helpful to the surgeon in evaluating how the force datachanges as the joint is extended and flexed providing both kinematic andkinetic information.

Alternatively or additionally, processing system 150 may providegraphical output data on a user interface 970 associated with gapmeasurement module 800. According to one exemplary embodiment, userinterface element 900 may include a chart 971 that provides respectivegauges indicating the relative magnitude of medial and lateral gapdistances 972 a, 972 b. Alternatively or additionally, chart 971 mayinclude a field 973 that displays the location (medial/lateral) andvalue of a relative imbalance in the geometric gap at the tibiofemoralinterface.

FIGS. 12-16 provide exemplary screen shots illustrating different waysthat processing system 150 can present information to a user of kneebalancing system 100. For example, FIG. 12 illustrates an exemplaryscreen shot 1200 that displays monitoring load magnitude and locationinformation for predetermined angles of joint flexion. As illustrated inFIG. 12, processing system 150 can compile, in tabular form, the medialand lateral load magnitude data (as well as the difference information(illustrated as AD-L in FIG. 120) at flexion angles of 0°, 45°, 90°, and120°. Processing system 150 can prepare this information for output on adisplay screen (of a computer or tablet device) in the operating room,so that the surgeon can evaluate the intra-operative performance of theknee joint.

According to another embodiment, processing system may compile, intabular form, the medial and lateral load location information (relativeto the anterior-posterior of force sensing module 130, as denoted byletters A, C, and P, where A is “anterior”, C is “center”, and P is“posterior”) at flexion angles of 0°, 45°, 90°, and 120°. Processingsystem 150 may also determine the difference in rotation between themedial and lateral load centers with respect to medio-lateral axis ofthe knee. Processing system 150 can aggregate this information andrender it for output on a display during the surgical procedure.

As an alternative or in addition to the tabular format illustrated inFIG. 12, processing system 150 may be configured to provide the medialand lateral load location and magnitude data overlaid atop a virtualrepresentation of force sensing module 150. In the exemplary screen shot1300, processing system 150 can provide user interfaces 1310, 1320,1330, and 1340, which contains substantially the same informationillustrated in the exemplary screen shot 1200 of FIG. 12, except theinformation is graphically overlaid atop an image representation offorce sensing module 130.

FIG. 14 provides an exemplary screen shot 1400 that provides a summaryview of the magnitude and anterior-posterior location of the load atpredetermined flexion angles. As illustrated in FIG. 14, processingsystem 150 may provide a user interface that illustrates the location ofthe load center detected in both the medial and lateral portions offorce sensing module 130 at flexion angles of 0°, 45°, 90°, and 120°.Whereas screen shot 1300 of FIG. 13 illustrates this information inseparate user interfaces 1310, 1320, 1330, and 1340, screen shot 1400provide this information in a single, “summary”-type format, with circlesizes and/or colors used to denote the load magnitude instead of printedvalues.

FIG. 15 provides an exemplary screen shot 1500 that provides bothinstantaneous tracking information of load location and magnitude, aswell as historic information as the joint is flexed and extended. Forexample, processing system 150 may display the instantaneous (i.e.,real-time) relative magnitude (indicated by the numerical chart belowthe graphical representation of the force sensing module 130), locationinformation (indicated by the “circles” in the medial and lateralportions of force sensing modules), and flexion angle (15°). Inaddition, certain previously-measured data (such as the location data)may be tracked and overlaid in the medial and lateral portions of theuser interface, to provide the surgeon with a view of the amount bywhich the location of the center of the load changes as the joint isflexed and extended.

Processing system 150 may also be configured to post-operativelyaggregate results for a number of different patients that were measuredduring intra-operative analysis of the knee joint. For example, screenshot 1600 illustrates an exemplary user interface 1610 that displaysintra-operative load data at various flexion/extension angles for anumber of different patients. This data can be coupled withpost-operative surveys in order to ascertain correlations between theintra-operative load testing data and final joint performance andpatient satisfaction information (in this embodiment, using the WOMACindex). This type of analysis may be particularly useful in allowingsurgeons to identify, using information for a variety of patients,specific load balance combinations and tolerances that result in maximumpatient comfort and performance.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed systems andassociated methods for measuring performance parameters in orthopedicarthroplastic procedures. Other embodiments of the present disclosurewill be apparent to those skilled in the art from consideration of thespecification and practice of the present disclosure. It is intendedthat the specification and examples be considered as exemplary only,with a true scope of the present disclosure being indicated by thefollowing claims and their equivalents.

What is claimed is:
 1. A force and orientation sensing system formeasuring performance parameters associated with an orthopedic articularjoint, comprising: a force sensing module comprising: a housingincluding an articular surface having a medial portion and a lateralportion, each of which is substantially mechanically isolated from theother; a first set of sensors disposed within the housing, the first setof sensors being mechanically coupled to the medial portion of thearticular surface and configured to detect information indicative of afirst force incident upon the medial portion of the articular surface;and a second set of sensors disposed within the housing, the second setof sensors being mechanically coupled to the lateral portion of thearticular surface and configured to detect information indicative of asecond force incident upon a lateral portion of the articular surface,and an orientation sensing module comprising a first orientation sensorand a second orientation sensor, wherein the orientation sensing moduleis configured to detect, via the first and second orientation sensors, arelative orientation of at least two bones associated with the articularjoint, wherein the articular joint is an articular joint of a lowerextremity of a patient.
 2. The force and orientation sensing system ofclaim 1, further configured to estimate, based at least in part on forcevalues detected by the first set of sensors, a magnitude and a locationof a center of force associated with the first force incident upon themedial portion of the articular surface.
 3. The force and orientationsensing system of claim 1, wherein the second set of sensors includes aplurality of transducers, each transducer including: a respectivecantilever component at least a portion of which is configured to deformin response to the second force incident upon the lateral portion of thearticular surface; and a respective strain gauge coupled to therespective cantilever component and configured to measure thedeformation in the respective cantilever component; wherein at least aportion of each cantilever component associated with the plurality oftransducers is mechanically supported at a proximal end by a centralbase component.
 4. The force and orientation sensing system of claim 1,further comprising a wireless transceiver configured to wirelesslytransmit the information indicative of the first and second forces to aremote processing module.
 5. The force and orientation sensing system ofclaim 1, wherein at least one of the first and second orientationsensors is an inertial measurement unit.
 6. The force and orientationsensing system of claim 1, wherein at least one of the first and secondorientation sensors are located outside the articular joint.
 7. Theforce and orientation sensing system of claim 1, wherein the orientationsensing module is located outside the articular joint.
 8. The force andorientation sensing system of claim 1, wherein the orientation sensingmodule is configured to detect, via each of the first and secondorientation sensors, a respective relative orientation of a bone withrespect to a reference orientation.
 9. The force and orientation sensingsystem of claim 8, wherein the orientation sensing module is furtherconfigured to detect an angular relationship between the at least twobones associated with the articular joint.
 10. The force and orientationsensing system of claim 9, wherein the angular relationship is at leastone of a flexion-extension angle, a varus-valgus angle, or a rotationangle.
 11. The force and orientation sensing system of claim 9, furthercomprising a processing device communicatively coupled to theorientation sensing module and configured to compute, based at least inpart on the respective relative orientations of the bones, the angularrelationship.